BIOL 1840U Lecture Notes - Proximal Tubule, Epithelium, Sodium Chloride

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29 Jan 2013

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Outline of Lecture 01 (04-24 B; Guggino)
Overview of Renal System
I. Functions of the human kidney
- Main function: maintain volume and solute concentration in extracellular fluid
- Also, excrete substances, make glucose, NH3, and hormones
II. Control of fluid compartments
- Fluid is compartmentalized in the human body
- Intracellular fluid: holds about 2/3 of body fluid
- Extracellular fluid: holds about 1/3 of body fluid
- Divided into interstitial, intravascular, and transcellular fluids
- Water is freely exchangeable among all body compartments, but distribution is controlled:
- By solute concentration (a colligative property), and
- By hydrostatic pressure
- Solute distribution is controlled
- By permeability
- By transporters
- For ions, by ion pumps (a transporter) and membrane potential
- Intracellular volume is controlled by each cell by regulating solute concentration
- e.g. by regulating Na and K concentration via the Na/K pump
- Extracellular volume and solute concentration is controlled by epithelia
- Inflow is controlled by GI epithelia
- Outflow is controlled by kidney (and sweat)
III. Homeostasis (control theory)
- In physiology, steady state about a set point is called homeostasis
- Maintaining homeostasis requires sensors, mediators, and effectors
- Key numbers (conc, mEq/L): Na 142, K 4.3, Ca 5, Cl 104, HCO3 24, (pCO2 40 mmHg, pH 7.4)
- Intracellular fluid is high in K and low in Na and Cl; extracellular fluid is the reverse
IV. Overview of renal structure/function
- See p. 11 for list of structure names (I assume here that you know this already)
- Renal function can be divided into three main processes: filtration, secretion, reabsorption
- Kidney receives 25% of total blood flow; huge amounts (180 L/day) are filtered and most of this
(all but 1-2 L/day) is reabsorbed
- Most reabsorption occurs in the proximal convoluted tubule
- Secretion is an active transport mechanism of excretion, occurs in the PCT
- Loop of Henle is involved in control of sodium/osmole conc. in medulla
- DCT and collecting ducts reabsorb NaCl and water
Summary of major points
- See Key Topics on p.17
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